verb. (media-jacking, media-jacked, media-jacker)
Using the term "jack" (used here as "to steal") this refers to the situation in which one person is using one medium (of entertainment or otherwise) and another person 'jacks' the other person's attention to another medium.

For example, when one person is listening to music and playing on the computer and another person puts on a movie for the first person to watch.

Person one (the "media-jacker") -"Hey watch this awesome movie!"
Person two-"Aw, dude can't it wait? I'm facebooking and got some music on."
*movie begins, audibly trumping the music and dominating the attention of person two*